I really enjoyed this story and can't believe no one has commented on it yet. I loved the alienness of the alien. I loved the interesting constraints on how the alien perceived (or didn't) our world and it's inhabitants. And I loved the way the MC dealt with the threat in the end.
Also, as much as I love the concept of the Rule of Three, I'm not sure I would want a society that lives by that rule. So much of what defines humanity is built by groups and coalitions, sometimes over generations. I don't think I would want to remove that aspect from our society.